How health advocates and industry actors attempt to assert their authority as a strategy of influence in policymaking remains underexplored in the health governance literature. Greater exploration of the kinds of authority sources used by health actors vis-à-vis market actors and the role ideational factors may play in shaping access to these sources provides insight into advocates' efforts to exert influence in policy forums. Using the trade domain in Australia as a case study of the way in which the commercial determinants of health operate, we examined the different ways in which health, public interest and market actors assert their authority. Drawing on a political science typology of authority, we analysed 87 submissions to the Australian government during the Trans-Pacific Partnership negotiations. We identify four types of authority claims; institutional authority, derived from holding a position of influence within another established institution; legal authority through appeals to legal agreements and precedents; networked authority through cross-referencing between actors, and expert authority through use of evidence. Combining these claims with a framing analysis, we found that these bases of authority were invoked differently by actors who shared the dominant neoliberal ideology in contrast to those actors that shared a public interest discourse. In particular, market actors were much less likely to rely on external sources of authority, while health and public interest actors were more likely to appeal to networked and expert authority. We argue that actors who share strong ideational alignment with the dominant policy discourse appear less reliant on other sources of authority. Implications of this analysis include the need for greater attention to the different strategies and ideas used by industry and public health organisations in trade policy agenda-setting for health, which ultimately enable or constrain the advancement of health on government agendas.